Despite the success of the naive ensemble usage of mid-level representations [1]}, nevertheless,
the mid-level representations considered in the prior works usually focus on spatial features extracted from a single frame, and dedicated little attention to the significance of temporal features concealed between multiple frames. Although a few researchers [2]}, [3]} proposed to incorporate optical flow as a type of temporal feature to represent the displacements of pixels, they overlook the essential properties and characteristics of optical flows. As a result, such a type of mid-level representation still leaves room for improvement, since it is unable precisely describe the temporal information of the objects in a scene.
